Brachytherapy, as is well known in the art, is a type of radiation therapy in which radioactive materials (variously referred to hereafter as “seeds” or “sources”) are placed in close proximity to, and often in direct contact with, the (typically malignant) tissue being treated. In very general terms, there are two currently practised brachytherapy treatments: low dose rate (LDR) treatments and high dose rate (HDR) treatments.
In low dose rate (LDR) treatments, sources with a relatively low radioactivity are permanently implanted within a tissue to be treated and left there to irradiate the tissue over the weeks and months following the implantation. In high dose rate (HDR) treatments, more highly radioactive sources are advanced into a tissue to be treated for a relatively short period of time, and then withdrawn from the patient once the treatment plan for that patient has been completed.
Brachytherapy treatment is appropriate for a variety of different conditions, including inter alia, prostrate tumours, breast tumours, lung cancer, oesophageal cancer, gynaecologic cancers (such as cervical cancer), anal/rectal tumours, sarcomas and head or neck cancers.
By way of illustration of the need for appropriate treatments for such conditions, in the UK over 10,000 patients per year are diagnosed with cancer of the rectum, and over 30% of the patients who have operable tumours subsequently require the use of a colostomy bag for the rest of their life.
Increasingly HDR brachytherapy is used to treat cancer of the rectum, in some instances before conventional surgical procedures are undertaken, and more recently an alternative to those surgical procedures (each of which has inherent risks associated with them). Recent studies of the use of HDR brachytherapy for the treatment of anal or rectal tumours have shown that the use of HDR brachytherapy can significantly reduce the likelihood of the patient having to be provided with a stoma.
In a commonplace HDR brachytherapy treatment (hereafter referred to simply as HDR brachytherapy), a plurality of catheters are inserted into the tissue to be treated, and a machine (known as “an afterloader”) is controlled by computer to push a single relatively highly radioactive seed (for example of Iridium 192) into each of the catheters. The computer moves the seeds through the catheters in accordance with a patient treatment plan that has been carefully devised to provide an appropriate irradiation dose distribution for the tissue of the particular patient undergoing treatment. The plan defines (for each radioactive seed) a plurality of longitudinal positions within the catheter to which the seed will be moved (the so-called “dwell positions”), and the time that the seed will remain at each of those locations (the so-called “dwell time”).
To implement the plan, the computer controls the afterloader to move each of the seeds to a first planned dwell position, to leave the seed at that position for the planned dwell time for that position, and then to move the source to the next planned position. This process is repeated until the dose distribution planned for treatment of the patient's tissue has been achieved.
A variety of systems have been developed to implement HDR brachytherapy, and an illustrative example of one such system is the so-called OncoSystem™ (sold by Nucletron UK Ltd (a Delft Instruments Company) of Nucletron House, Chowley Oak, Tattenhall, Chester CH3 9EX, United Kingdom). The OncoSystem™ consists of a bundle of Nucletron products for treating body-site specific cancers such as breast, rectal or gynecological cancers, and each bundle consists of OncoSmart™ applicators and disposables, and an Oncentra™ treatment control system.
The OncoSystem™ provides an accurate method of positioning sources inside the patient. However, a significant drawback of the system (and other like systems) is that measurement of the actual dose (as opposed to the planned dose) delivered to the patient is accomplished externally of the patient, and as such in a number of applications is necessarily somewhat inaccurate, principally because there is often a significant amount of tissue (often with varying radiation absorption properties) between the tumour and the skin.
The combination of technological complexity, a relatively large number of patients and the potentially hazardous nature of ionising radiation mean that there is a great potential for serious accident with potentially serious consequences if HDR brachytherapy is incorrectly delivered. To reduce, and preferably avoid, such problems—in particular damage to tissue surrounding the tumour being treated—it is important to know how much radiation is being delivered during treatment, and where that radiation is being delivered. The UK National Cancer Standard dictates that in vivo dosimetry should be performed for all types of radiation treatments, but as yet there is no effective in vivo dose measurement device available which could be used to measure how much radiation is actually being delivered during HDR Brachytherapy.
An aim of the present invention is to provide an in vivo dose detector for HDR brachytherapy, and an HDR brachytherapy system with which the detector can be used. It is anticipated that by virtue of the teachings of the present invention, it will be possible to further enhance HDR brachytherapy to the benefit of patients.